In baseball, an off-speed pitch that moves in the opposite direction of a curveball or a slider.
To achieve a screwball grip, a pitcher must grip the baseball like a four-seam fastball, with the index and middle fingers on the widest part of the seam. The thumb rests underneath the ball, and the ring and pinky fingers hug the ball to the side. The ball is held away from the palm and the wrist is twisted inwards (rather than outwards as with a curveball) as the pitcher releases the ball. This creates a pitch that moves in the reverse direction of a traditional curveball or slider. A right-handed pitcher will throw a screwball down and in to a right-handed batter and away from a left-handed batter. Likewise, a screwball from a left-handed pitcher will have the opposite effect. When used with other off-speed pitches, the screwball can be effective at catching batters off-guard. A pitcher can also create sinking action with a screwball by changing the angle of his arm during release.